Electromagnetically actuated valve, especially for hydraulic braking systems in motor vehicles

ABSTRACT

The valve ( 10 ) has a seat valve ( 27 ) comprising a hollow cone-shaped valve seat ( 24 ) and an hemispherical shutoff element ( 26 ). An afflux bore ( 23 ) having contact with a pressure-medium inlet ( 19 ) discharges centrically into the valve seat ( 24 ). A solenoid armature ( 30 ) acting upon the seat valve ( 27 ) in opening fashion grips a push rod ( 25 ) comprising the shutoff element ( 26 ), which said solenoid armature cooperates with a pole body ( 42 ) according to the flat-type armature principle. A preloaded return spring ( 39 ) acting on the seat valve ( 27 ) in closing fashion is arranged between the pole body ( 42 ) and the solenoid armature ( 30 ).  
     The valve ( 10 ) works as a proportioning valve, because, in addition to a suitable design of the seat valve ( 27 ) and push rod ( 25 ), the magnetic force is infinitely variable and, together with a hydraulic force, has a monotonously increasing course as the valve opening stroke increases, while the spring force—which also has a monotonously increasing course as the valve opening stroke increases—has a positive slope that is greater than that of the course of the magnetic and hydraulic force.

RELATED ART

[0001] The invention is based on an electromagnetically actuated valveaccording to the general class in claim 1.

[0002] A valve is already known (DE 41 34 490 A1) that is designed as aproportioning pressure-control valve. To obtain good control behavior,the known pressure-control valve equipped with a seat valve closedwithout current is designed according to the solenoid plunger principle,that is, the pole body has a recess on the front side into which thebasically cylindrical solenoid armature plunges more or less deeply as afunction of an electric current supplied to an electrical windingenclosing the pole body. The magnetic force acting upon the solenoidarmature is thereby supported by a hydraulic force in the sense ofopening the seat valve, while the force of the return spring counteractsthese forces.

[0003] The known valve has the disadvantage, however, that the solenoidplunger principle requires increased expenditures in the structuraldesign of the pole body and solenoid armature. In particular, low radialtolerances are required between the solenoid armature and the pole bodyto prevent the formation of secondary air gaps. This, in turn, requiresa costly guidance of the solenoid armature with low guidance play,because transversal forces on the solenoid armature can lead tofunctional failings. The known valve is therefore costly to manufacture.

[0004] Moreover, an electromagnetically actuated valve operatingaccording to the flat-type armature principle is made known in DE 196 04317 A1 that comprises a seat valve that is open in the non-energizedstate. Although this known valve is designed like a two-position valve(open, close valve), it can be moved into numerous random intermediatepositions using short strokes like a proportioning valve by controllingthe magnetic force that counteracts the force of a return spring and ahydraulic force, without having to comprise the expensive design of aproportioning valve, however. The main contributing features here arethe design of the seat valve and the coordination of the magnetic forcecharacteristic curve and return spring.

ADVANTAGES OF THE INVENTION

[0005] In contrast to the proportioning valve mentioned initially, theelectromagnetically actuated valve according to the invention having thefeatures in claim 1 has the advantage that it has the simple design of atwo-position valve with a flat-type armature but behaves like aproportioning valve. Since, with the flat-type armature, the lines offlux of the magnetic circuit in the working air gap basically extendbetween the facing-each-other, flat front sides of pole body andsolenoid armature, radial tolerances have little effect in this design.Moreover, the design of the seat valve and push-rod region contributesto a stable control behavior of the valve according to the inventionworking as pressure-control valve: the pressure prevailing on the sideof the pressure-medium inlet supports the magnetic force to open theseat valve. Pressure medium emerging from the valve seat is directedwithout turbulence along the shutoff member and the push rod against thesolenoid armature and exerts an opening effect. As the pressuredifferential between pressure-medium inlet and pressure-medium outletdecreases, this force effect diminishes, and the valve reaches a stablefinal position of the seat valve when the pressure at the outletadjusted as a function of flow is reached. This control procedure takesplace with dynamics and control quality that suffices for manyapplications.

[0006] An advantageous design of the valve according to the invention isdescribed in claim 2.

BRIEF DESCRIPTION OF THE DRAWING

[0007] A simplified version of an exemplary embodiment of the inventionis shown in the drawing and described in greater detail in thesubsequent description.

[0008]FIG. 1 shows a longitudinal view of an electromagneticallyactuated valve having a seat valve. In contrast to FIG. 1,

[0009]FIG. 2 shows an enlarged view of the seat valve situated in theclosed position in the non-energized state.

[0010]FIG. 3 shows a diagram of the forces acting in the valve along thevalve opening stroke.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0011] An electromagnetically actuated valve 10 shown in the drawing inFIG. 1 for hydraulic brake systems in motor vehicles, e.g., power-brakesystems according to DE 195 46 647 A1, basically comprises twoassemblies: a hydraulic portion 13 secured in a stepped bore 11 of avalve block 12, and an electrical portion 14 fitted onto the hydraulicportion.

[0012] The hydraulic portion 13 of the valve 10 has a longitudinallypenetrating valve body 16 that is connected to an armature guide sleeve17. The valve body 16 and the armature guide sleeve 17 are secured inthe stepped bore 11 of the valve block 12 by means of a first caulkedjoint 18. The valve body 16 comprises a pressure-medium inlet 19 of thevalve 10 that is connected to an afflux passage 20 for dischargingpressure medium at the base of the stepped bore 11. A filter disc 21 issituated in the stepped bore 11 between the pressure-medium inlet 19 andthe afflux passage 20.

[0013] The valve body 16 is provided with an afflux bore 23 in theregion opposite to the base of the bore, which said afflux boretransitions into a hollow cone-shaped valve seat 24. An hemisphericalshutoff element 25 formed on a push rod 25 is coordinated with the valveseat 24. The valve seat 24 and the shutoff element 26 form a seat valve27 that is described in greater detail further below using FIG. 2.

[0014] In the armature guide sleeve 17, a valve chamber 29 abuts thevalve body 16, in which said valve chamber a solenoid armature 30 islongitudinally moveably guided. The solenoid armature 30 basically hasthe design of a straight circular cylinder with radially extending frontsides 31 and 32. The push rod 25 rises from the front side 31 facing thevalve body 16, which said push rod is pressed into the solenoid armature30 with a pin 33. The portion of the valve chamber 29 situated betweenthe valve body 16 and the solenoid armature 30 is connected to apressure-medium outlet 35 of the valve 10 by means of an opening 34 inthe armature guide sleeve 17 and further to a forward-flow passage 36 ofthe valve block 12 discharging into the stepped bore 11. Apart from thepush rod 25, the portion of the valve chamber 29 situated between thevalve body 16 and the solenoid armature 30 contains no installed parts.

[0015] The solenoid armature 30 has relatively great radial play inrelation to the armature guide sleeve 17. Said solenoid armature isprovided with two longitudinal grooves 38 extending along its entirelength. A return spring 39 in the form of a helical compression springis accommodated in the solenoid armature 30 in the region of its frontside 32 opposite to the valve body 16. This said return spring hasrelatively great stiffness and grips a residual air gap disc 40 withpreload, which said residual air gap disc is supported on a radiallyextending front side 41 of a pole body 42. The pole body 42 engages withpart of its length in the armature guide sleeve 17, to which it isconnected in pressure-medium-tight fashion. A working air gap 43 whichdetermines the opening stroke of the valve 10 is located between thefront side 32 of the solenoid armature 30 and the residual air gap disc40.

[0016] A filter sleeve 45 situated between the pressure-medium outlet 35and the forward-flow passage 36 is accommodated in the stepped bore 11of the valve block 12 on the jacket side of the armature guide sleeve17. In the direction toward the outlet of the stepped bore 11, this saidfilter sleeve is followed by a sealing ring 46, a disc 47 and a bushing48 that is secured by means of a second caulked joint 49 in the steppedbore 11 of the valve block 12.

[0017] The electrical portion 14 fitted onto the hydraulic portion 13 ofthe valve has a coil 52 with an electrical winding 53 enclosed in ahousing 50 with a washer 51. While the housing 50 radially inwardlyabuts the pole body 42, the washer 51 establishes a connection with thebushing 48.

[0018] The solenoid armature 30, the pole body 42, the bushing 48, thehousing 50, and the washer 51 are composed of magnetically conductivematerial, while the armature guide sleeve 17 and the residual air gapdisc 40 are not magnetically conductive. A magnetic circuit producedwhen current is supplied to the electrical winding 53 extends over thepole body 42, the residual air gap disc 40, the solenoid armature 30,the armature guide sleeve 17, the washer 51, and the housing 50 of theelectrical portion 14. The solenoid armature 30 and the pole bodythereby cooperate according to the flat-type armature principle.

[0019] The region of the seat valve 27 that is important to the functionof the valve 10 as a pressure-control valve comprises the followingdesign features, which are described using FIG. 2:

[0020] The hollow cone-shaped valve seat 27 has a cone angle α, whichdoes not exceed 75°. The valve seat 24 is delimited with sharp edgesfrom the valve chamber 29 by means of a flat recess 55 in the valve body16. The radius R₁ of the hemispherical shutoff element 26 is coordinatedwith the valve seat 24 in such a fashion that the diameter D₁ of theafflux bore 23 nearly corresponds to the seal diameter D₂ of the seatvalve 27. A relatively short cylindrical portion 56 of the push rod 25follows the shutoff element 26. The cylindrical portion 56 has adiameter D₃ that corresponds to twice the radius R₁ of the shutoffelement 26. A cone-shaped portion 57 of the push rod 25 against thesolenoid armature 30 steplessly abuts the cylindrical portion 56. Thissaid cone-shaped portion has a cone angle β of approximately 35° andsteplessly transitions with rounded transition having the radius R₂ intothe front side 31 of the solenoid armature 30.

[0021] A pressure P₁ prevails in the afflux bore 23, which said pressureis provided by a high-pressure pump or a pressure-medium accumulator ifthe valve 10 is used in the initially-mentioned power-brake system. Apressure P₂ of between the value 0 and P₁ can prevail in the valvechamber 29.

[0022] The electromagnetically actuated valve 10 operates as follows:

[0023] The starting point is a non-energized state of the electricalwinding 53, so that the seat valve 27 assumes its closed position (asshown in FIGS. 1 and 2). A relatively high pressure P₁ prevails on theafflux side of the seat valve 27, and a very low pressure P₂ prevails onthe forward-flow side. The preloaded return spring 39 exerts a force fon the solenoid armature 30 and the push rod 25 that holds the seatvalve 27 in the closed position up to a permissible maximum value of thepressure P₁. In the diagram shown in FIG. 3—which shows the course ofthe forces F acting in the valve 10 along the valve opening stroke,namely spring force F_(F), magnetic force F_(M), and hydraulic forceF_(p)—this preload force f of the spring 39 is plotted on the ordinateat 0 travel. In the diagram, the course of the spring force F_(F)exerted by the return spring 39 is shown as a straight line, the courseof which increases monotonously as the valve opening stroke H increases.The high stiffness of the return spring 39 determines the relativelyhigh slope of the spring force characteristic curve. The secondcharacteristic curve represents the course of the magnetic force F_(M)and hydraulic force F_(p)—which are combined in cumulative fashion—at aconstant current I and a constant pressure differential δ_(p) betweenthe pressures p₁ and p₂. The characteristic curve F_(M)+M_(p) has acourse that increases monotonously as the valve opening stroke Hincreases, the slope of which said course is less than that of thecharacteristic curve F_(F), however. This relatively flat course of thecharacteristic curve F_(M)+F_(p) is basically achieved by the layout ofthe magnetic circuit and, in fact, by means of a relatively greatworking air gap 43 and a relatively thick residual air gap 40.Additionally, the effect of the hydraulic force F_(p) on the push rod 25and solenoid armature 30 is kept to a minimum by the fact that the sealdiameter D₂ is relatively small, and by the fact that pressure mediumflows around all sides of the solenoid armature 30. The working point APof the valve 10 is located at the intersection of the two characteristiccurves, at which said working point the seat valve 27 assumes a workingstroke h. By changing the current I applied to the electrical winding 53of the coil 52, the characteristic curve F_(M)+F_(p) is capable of beingshifted in the diagram and, accordingly, the working point AP is capableof being adjusted to a different stroke h.

[0024] When current is applied to the electrical winding 53 of the coil52, the magnetic force F_(M) acts upon the solenoid armature 30 in anopening fashion. The hydraulic force F_(p) represented by the pressuredifferential p₁−p₂ also has an opening effect on the push rod 25. Theforce F_(F) of the return spring 30 acting, in contrast, in a closingfashion is overcome when the current I is sufficiently high and opensthe seat valve 27. Pressure medium flows from the pressure-medium inlet19 to the pressure-medium outlet 35 of the valve 10. In this process,pressure medium flows along the push rod 25 toward the front side 31 ofthe push rod and solenoid armature 30 and exerts an opening effect onthese. As the pressure p₂ in the valve chamber 29 increases, a pressureimbalance occurs at the solenoid armature 30 that reduces the hydraulicforce F_(p) acting in opening fashion. The spring force F_(F) exerted bythe return spring 30 moves the seat valve 27 into the closed positionwhen the forward-flow side pressure p₂ coordinated with the electriccurrent I is reached. Due to the design of the valve 10, theforward-flow side pressure p₂ is proportional to the current I appliedto the electrical winding 53.

[0025] The electromagnetically actuated valve 10 is self-stabilizingwhen minor disruptions occur:

[0026] The working point AP of the valve 10 is assumed when anequilibrium of forces between the magnetic force F_(M), the hydraulicforce F, and the spring force F_(F) is given. Disruptions in thisequilibrium of forces, caused by fluctuations in hydraulic force F_(p),for instance, only lead to a short-term shifting of the working pointAP: an increase in the hydraulic force F_(p) therefore leads to anextension of the valve opening stroke H, with the consequence that thespring force F_(F) increases at the same time. Although this initiallyresults in a shifting of the working point AP on the spring forcecharacteristic curve F_(F), it is offset by the return of the solenoidarmature 30 by means of the spring force F_(F) on the working stroke hafter the hydraulic disruption is eliminated, however.

[0027] In the non-energized state, the valve 10 is also capable of beingused as a pressure-relief valve:

[0028] If pressures p₁ prevail at the pressure medium inlet 19 thatproduce an hydraulic force F_(p) acting in opening fashion that is lessthan the preload force f of the return spring 39, the seat valve 27remains in its closed position. If, on the other hand, the preload forcef of the return spring 39 is overcome at higher pressures, the seatvalve 27 opens, and pressure medium can flow forward from thepressure-medium inlet 19 of the valve 10 to its pressure-medium outlet35 with a pressure-relieving effect.

What is claimed is:
 1. An electromagnetically actuated valve (10), inparticular for hydraulic brake systems in motor vehicles, having thefollowing features: a seat valve (27) closed without current is arrangedbetween a pressure-medium inlet (19) and a pressure-medium outlet (35),the seat valve (27) has a hollow cone-shaped valve seat (24) and anhemispherical shutoff element (26) formed on a push rod (25), an affluxbore (23) having contact with the pressure-medium inlet (19) dischargescentrically into the valve seat (24), a solenoid armature (30) actingupon the seat valve (27) in opening fashion grips the push rod (25),with which said solenoid armature a pole body (42) corresponds on theside opposite to the push rod, a preloaded return spring (39) acting onthe seat valve (27) in closing fashion is supported at the solenoidarmature (30), characterized by the further features: the diameter (D₁)of the afflux bore (23) nearly corresponds to the seal diameter (D₂) ofthe seat valve (27), the cone angle (α) of the valve seat (24) does notexceed 75°, pressure medium emerging from the valve seat (24) is capableof being conducted steplessly along the push rod (25) to a radiallyextending, largely flat front side (31) of the solenoid armature (30)with rounded transition between push rod (25) and solenoid armature(30), the solenoid armature (30) and the pole body (42) cooperateaccording to the flat-type armature principle, the magnetic circuit ofthe valve (10) is designed such that the magnetic force (F_(M)) exertedon the solenoid armature (30) and transmitted to the shutoff element(26) is infinitely variable, whereby its course increases monotonouslyas the valve opening stroke (H) increases together with a hydraulicforce (F_(p)) produced by the pressure medium and acting upon shutoffelement (26) and solenoid armature (30), the force (F_(F)) produced bythe return spring (39) on the shutoff element (26) is set such that ithas a course that increases monotonously as the valve opening stroke (H)increases, the positive slope of which is greater than that of thecourse of the magnetic and hydraulic force.
 2. The valve according toclaim 1, wherein the hemispherical shutoff element (26) is integrallymolded in stepless fashion on a cylindrical portion (56) of the push rod(25), which said cylindrical portion is followed in stepless fashion onthe side opposite to the valve seat by a cone-shaped portion (57) of thepush rod (25) having low conicity, against which said cone-shapedportion a radially extending front side (31) of the push rod (25) and/orof the solenoid armature (30) abuts after a transition radius (R₂).